The active site in the wild type turkey third domain ovomucoid (OMTKY3) protein is occupied by a hydrophobic leucine residue (Leu18). This residue is directly involved in the specific binding to the chymotrypsin pocket in the complex form. The goal of this project is to compare the pKa of nearby His57 in chymotrypsin in mutant-OMTKY3-chymotrypsin complexes. We are investigating Leu18?Ala and Leu18?G mutations, where the active side chain (Leu18) in OMTKY3 is changed to small non-ionizing groups. We have already made the G18 mutation and are preparing the protein in order to do 1D NMR experiments at different pH values. This will allow us to measure the pKa value of His57 in the wild type and mutant OMTYKY3 in the complex form and correlate the effect of mutation to the Kassoc measured by Laskowski's group.